This invention relates to an improved dye penetrant composition and method for non-destructively testing material specimens to locate and identify surface voids, cracks or defects, and more particularly to an improved liquid vehicle for such a dye penetrant. The invention is especially concerned with a novel easily water washable, stable and sensitive dye penetrant composition of the above type having the characteristics of being able to disclose a wide range of defective conditions in parts, employing as solvent or vehicle essentially a biodegradable nonionic surfactant in the form of certain combinations or mixtures of certain ethoxylated alcohols; and to a method utilizing such dye penetrant composition for non-destructive testing of parts.
In known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in test bodies or parts, a dye penetrant composition, preferably containing a fluorescent dye, and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the fluorescent dye, which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions, such as invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks and flaws, as well as intermediate size and gross cracks, it is necessary that the dye penetrant composition have high sensitivity.
Volatile type solvents are commonly employed for extending or thinning dye penetrant inspection solutions or compositions. This is done chiefly for the purpose of lowering the viscosity of the penetrant in order to adapt it for application in spraying systems. Thus for example solvents such as kerosene, light fuel oils, and methyl ethyl ketone, all highly volatile solvents, have heretofore been employed in prior art dye penetrants. See for example U.S. Pat. NO. 2,806,959. Further, most dye penetrant solutions in practice generally require the use of a combination of solvents, including primary and secondary solvents, extender solvents and wetting agents.
However, the use of volatile solvents in dye penetrant compositions has certain disadvantages. Thus, the use of volatile solvents in dye penetrants results in the evolution of fumes and solvent vapors which are rapidly formed by the evaporating solvent.
In addition, stability of the penetrant solution is essential without the necessity for carefully balancing the various liquid components of a dye penetrant solution in order to obtain efficient penetration of the solution into the cracks and flaws of a part, dye solubility, wetting action and washability control.
An additional criterion has recently developed also with respect to dye penetrant solutions and compositions. Generally, dye penetrant solutions presently being used and containing solvents and wetting agents present a disposal problem in that they are substantially non-biodegradable, that is, they are very difficult to decompose by bacteria in sewage disposal plants. Hence the necessity for the development of dye penetrant solutions and compositions which are biodegradable, that is which employ dye solvents and carriers which are biodegradable, and are readily available despite the petrochemical shortage, has attained considerable importance.
In my U.S. Pat. No. 3,915,886 there is disclosed a novel dye penetrant which has improved washability and sensitivity characteristics, and which is biodegradable, containing as the vehicle for the dye, certan biodegradable nonionic ethoxylated alcohols. Although dye penetrants of this type have been tested extensively and have proved highly satisfactory and effective for most applications, occasionally some undesirable fluorescent background was left on the parts undergoing inspection. Also, although high sensitivity formulations can be provided by means of the penetrant compositions of my above application, including the aforementioned nonionic ethoxylated alcohols as surfactant, in some instances an even greater sensitivity range is desired for the dye penetrant, especially when working with parts or specimen containing a wide range of cracks or defects of varying sizes. Also, it has been found that when employing many of the nonionic ethoxylated alcohols in dye penetrants according to my U.S. Pat. No. 3,915,886, it is necessary to employ relatively high volumes of water and increased pressure to wash excess penetrant from the surface of the test specimen.
Accordingly, an object of the present invention is the provision of a readily water washable dye penetrant solution or composition which avoids the use of the conventional primary and secondary volatile and non-volatile solvents, and multiplicity of wetting agents, and their above-noted disadvantages, and which is highly stable, has excellent sensitivity and is essentially non-flammable and non-toxic. A particular object of the invention is to provide a dye penetrant solution of the above-noted type, having good wettability characteristics, and which employs a liquid carrier or vehicle for the dye, which is generally of the type disclosed in my U.S. Pat. No. 3,915,886, which is readily available and is biodegradable, thus rendering the dye penetrant solution essentially biodegradable, and which has certain additional advantages.